U.S. patent application number 16/507853 was filed with the patent office on 2021-01-14 for multiple port network device with differential ports for reduced electromagnetic interference at optical modules.
This patent application is currently assigned to CISCO TECHNOLOGY, INC.. The applicant listed for this patent is CISCO TECHNOLOGY, INC.. Invention is credited to Alpesh U. Bhobe, Guangcao Fu, Jianquan Lou, Hailong Zhang, Xiaoxia Zhou.
Application Number | 20210014583 16/507853 |
Document ID | / |
Family ID | 1000004228103 |
Filed Date | 2021-01-14 |
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United States Patent
Application |
20210014583 |
Kind Code |
A1 |
Zhou; Xiaoxia ; et
al. |
January 14, 2021 |
MULTIPLE PORT NETWORK DEVICE WITH DIFFERENTIAL PORTS FOR REDUCED
ELECTROMAGNETIC INTERFERENCE AT OPTICAL MODULES
Abstract
In one embodiment, an apparatus includes a plurality of optical
module ports in communication with a physical layer device in a
network device. Communication of signals from the physical layer
device to the optical module ports is configured such that the
signals received at the optical module ports adjacent to one
another are at different phases to reduce electromagnetic
interference associated with the optical module ports.
Inventors: |
Zhou; Xiaoxia; (Shanghai,
CN) ; Zhang; Hailong; (Shanghai, CN) ; Lou;
Jianquan; (Shanghai, CN) ; Fu; Guangcao;
(Shanghai, CN) ; Bhobe; Alpesh U.; (Sunnyvale,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CISCO TECHNOLOGY, INC. |
San Jose |
CA |
US |
|
|
Assignee: |
CISCO TECHNOLOGY, INC.
San Jose
CA
|
Family ID: |
1000004228103 |
Appl. No.: |
16/507853 |
Filed: |
July 10, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04Q 11/0005 20130101;
H04B 10/58 20130101; H04Q 2011/0039 20130101; H04B 10/69
20130101 |
International
Class: |
H04Q 11/00 20060101
H04Q011/00; H04B 10/58 20060101 H04B010/58; H04B 10/69 20060101
H04B010/69 |
Claims
1. An apparatus comprising: a plurality of optical module ports in
communication with a physical layer device in a network device;
wherein communication of signals from the physical layer device to
the optical module ports is configured such that the signals
received at the optical module ports adjacent to one another are at
different phases to reduce electromagnetic interference associated
with the optical module ports.
2. The apparatus of claim 1 wherein a phase offset between the
adjacent optical module ports is approximately 180 degrees.
3. The apparatus of claim 1 wherein four of the optical module
ports are in communication with the physical layer device.
4. The apparatus of claim 1 further comprising a plurality of
physical layer devices, each of the physical layer devices in
communication with a group of the optical module ports.
5. The apparatus of claim 4 wherein the group of the optical module
ports in communication with one of the physical layer devices
operates at a phase offset from a group of the optical module ports
in communication with another one of the physical layer
devices.
6. The apparatus of claim 4 wherein a phase offset between the
physical layer devices is random.
7. The apparatus of claim 1 wherein a length of a trace between the
physical layer device and one of the optical module ports is
adjusted to provide said different phases at the adjacent optical
module ports.
8. The apparatus of claim 1 wherein an electrical parameter at the
physical layer device is adjusted to provide said different phases
at the adjacent optical module ports.
9. A switch comprising: a plurality of physical layer devices; and
a plurality of optical module ports in communication with said
plurality of physical layer devices; wherein communication of
signals from each of the physical layer devices to the optical
module ports is configured such that the signals received at the
optical module ports adjacent to one another are at different
phases to reduce electromagnetic interference associated with the
optical module ports.
10. The switch of claim 9 wherein a phase offset between the
adjacent optical module ports is approximately 180 degrees.
11. The switch of claim 9 wherein four of the optical module ports
are in communication with each of the physical layer devices.
12. The switch of claim 9 wherein a group of the optical module
ports in communication with one of the physical layer devices
operates at a phase offset from a group of the optical module ports
in communication with another one of the physical layer
devices.
13. The switch of claim 9 wherein a length of specified traces
between the physical layer devices and the optical module ports are
adjusted to provide said different phases between the adjacent
optical module ports.
14. The switch of claim 9 wherein electrical parameters at the
physical layer devices are adjusted to provide said different
phases between the adjacent optical module ports.
15. The switch of claim 9 wherein a phase offset between the
physical layer devices is random.
16. A method comprising: transmitting electrical signals from a
physical layer device to a plurality of optical module ports; and
offsetting phases between the electrical signals transmitted to the
optical module ports adjacent to one another to reduce
electromagnetic interference associated with the optical module
ports.
17. The method of claim 16 wherein a length of traces between the
physical layer device and one of the optical module ports is
adjusted to provide said phase offset between the adjacent optical
module ports.
18. The method of claim 16 wherein an electrical parameter at the
physical layer device is adjusted to provide said phase offset
between the adjacent optical module ports.
19. The method of claim 16 wherein said phase offset between the
adjacent optical module ports is approximately 180 degrees.
20. The method of claim 16 wherein four of the optical module ports
are in communication with the physical layer device.
Description
TECHNICAL FIELD
[0001] The present disclosure relates generally to multi-port
network devices, and more particularly, to reducing electromagnetic
interference (EMI) of multi-port network devices.
BACKGROUND
[0002] Optical transceiver modules are commonly used in switches
and routers. With the development of higher performance electronic
devices, system power, number of ports, and frequency continue to
increase, resulting in EMI challenges, especially with regard to
optical module cages and optical modules.
BRIEF DESCRIPTION OF THE DRAWINGS
[0003] FIG. 1 is schematic illustrating optical module ports in
communication with physical layer chips, in accordance with one
embodiment.
[0004] FIG. 2A is a schematic of the optical module ports shown in
FIG. 1 with adjusted trace length between the physical layer chip
and two of the optical module ports to provide phase offset between
adjacent ports, in accordance with one embodiment.
[0005] FIG. 2B is a schematic of the optical module ports shown in
FIG. 1 with modified electrical parameters at the physical layer
device to provide phase offset between adjacent ports, in
accordance with one embodiment.
[0006] FIG. 3A is a schematic front view of a simulation model for
a 2.times.2 optical cage.
[0007] FIG. 3B is a schematic rear view of the simulation model of
FIG. 3A with vertical polarization.
[0008] FIG. 3C is a schematic rear view of the simulation model of
FIG. 3A with horizontal polarization.
[0009] FIG. 4A is a schematic illustrating differential ports in a
2.times.4 arrangement.
[0010] FIG. 4B is a schematic illustrating differential ports in a
2.times.8 arrangement.
[0011] FIG. 4C is a schematic illustrating differential ports in a
2.times.24 arrangement.
[0012] FIG. 5A is a graph illustrating EMI reduction with the
differential ports shown in FIG. 3B.
[0013] FIG. 5B is a graph illustrating EMI reduction with the
differential ports shown in FIG. 3C.
[0014] FIG. 6 is a graph illustrating EMI reduction with the
differential ports shown in FIG. 4C.
[0015] FIG. 7A is a table illustrating random phase combinations
for differential port simulation.
[0016] FIG. 7B is a graph illustrating the random phase
combinations shown in FIG. 7A.
[0017] FIG. 8A is a graph illustrating EMI reduction with the
differential ports for a Random-1 phase input shown in FIGS. 7A and
7B.
[0018] FIG. 8B is a graph illustrating EMI reduction with the
differential ports for a Random-2 phase input shown in FIGS. 7A and
7B.
[0019] FIG. 8C is a graph illustrating EMI reduction with the
differential ports for a Random-3 phase input shown in FIGS. 7A and
7B.
[0020] FIG. 9 is a block diagram depicting an example of a multiple
port network device on which the embodiments described herein may
be implemented.
[0021] Corresponding reference characters indicate corresponding
parts throughout the several views of the drawings.
DESCRIPTION OF EXAMPLE EMBODIMENTS
Overview
[0022] In one embodiment, an apparatus generally comprises a
plurality of optical module ports in communication with a physical
layer device in a network device. Communication of signals from the
physical layer device to the optical module ports is configured
such that the signals received at the optical module ports adjacent
to one another are at different phases to reduce electromagnetic
interference associated with the optical module ports.
[0023] In one or more embodiments, a phase offset between the
adjacent optical module ports is approximately 180 degrees.
[0024] In one or more embodiments, four of the optical module ports
are in communication with the physical layer device.
[0025] In one or more embodiments, the apparatus further comprises
a plurality of physical layer devices, each of the physical layer
devices in communication with a plurality of the optical module
ports. In one or more embodiments, a group of the optical module
ports in communication with one of the physical layer devices
operate at a phase offset from a group of the optical modules in
communication with another one of the physical layer devices.
[0026] In one or more embodiments, a length of a trace between the
physical layer device and one of the optical module ports is
adjusted to provide the different phases at the adjacent optical
module ports.
[0027] In one or more embodiments, an electrical parameter at the
physical layer device is adjusted to provide the different phases
at the adjacent optical module ports.
[0028] In another embodiment, a switch generally comprises a
plurality of physical layer devices and a plurality of optical
module ports in communication with the plurality of physical layer
devices. Communication of signals from each of the physical layer
devices to the optical module ports is configured such that the
signals received at the optical module ports adjacent to one
another are at different phases to reduce electromagnetic
interference associated with the optical module ports.
[0029] In yet another embodiment, a method generally comprises
transmitting electrical signals from a physical layer device to a
plurality of optical module ports and offsetting phases between the
electrical signals transmitted to optical module ports adjacent to
one another to reduce electromagnetic interference associated with
the optical module ports.
Example Embodiments
[0030] The following description is presented to enable one of
ordinary skill in the art to make and use the embodiments.
Descriptions of specific embodiments and applications are provided
only as examples, and various modifications will be readily
apparent to those skilled in the art. The general principles
described herein may be applied to other applications without
departing from the scope of the embodiments. Thus, the embodiments
are not to be limited to those shown, but are to be accorded the
widest scope consistent with the principles and features described
herein. For purpose of clarity, details relating to technical
material that is known in the technical fields related to the
embodiments have not been described in detail.
[0031] Optical transceiver modules are used for high speed fiber
optic digital communications. Pluggable optical modules allow for
easy insertion (or extraction) of the transceivers into (or from)
an optical cage on a network device or line card. The optical
transceiver module and the optical cage (cage connector, housing)
are a common radiation source and contribute to EMI
(Electromagnetic Interference) leakage at a front of the network
device (location of optical connectors). With an increase in system
power, number of ports, and operating frequency, meeting EMI
requirements, including RE (Radiated Emission) tests becomes more
challenging. The superposition of multi-port radiation rapidly
worsens radiation performance. In general, more ports create bigger
challenges for radiation tests and EMC (Electromagnetic
Compatibility) compliance.
[0032] Examples for reducing EMI include shielding and absorption;
however, these both have drawbacks. For example, some seams are
needed for function, such as a latch of an SFP (Small Form-Factor
Pluggable) cage, which either cannot be shielded or is difficult to
shield. Due to the limited space availability, there may not be
sufficient space to add an RF (Radio Frequency) absorber. Also,
absorbers are expensive. These physical changes require additional
design time and verification testing, and increase manufacturing
costs.
[0033] The embodiments described herein set adjacent optical module
ports out of phase from one another to reduce EMI in multi-port
network devices without any increase (or no significant increase)
to cost. In one or more embodiments, an apparatus comprises a
plurality of optical module ports in communication with a physical
layer device in a network device. Communication of signals from the
physical layer device to the optical module ports is configured
such that the signals received at the optical module ports adjacent
to one another are at different phases to reduce electromagnetic
interference associated with the optical module ports. The offset
of phases at adjacent ports is referred to herein as differential
port.
[0034] Referring now to the drawings, and first to FIG. 1, an
example of physical layer devices (chips) (PHYs) 10 in
communication with SFP modules 12 is shown. The PHYs 10 are
connected to a common clock 14. For simplification, the SFP modules
12 are only shown for two of the physical chips 10 (Phy1 and Phy3).
Phy2 may similarly be in communication with SFP modules 12. It is
to be understood that the simplified schematic shown in FIG. 1 is
only an example and that the system (network device, network
equipment, line card, route processor card, etc.) may include any
number of PHYs 10, each in communication with any number of optical
modules 12 (e.g., SFP or any type of pluggable optical module).
[0035] The optical modules 12 (pluggable optical modules,
transceivers, optical transceivers) may comprise any type of
pluggable optical module in any form factor including, for example,
SFP (Small Form-Factor Pluggable), QSFP (Quad Small Form-Factor
Pluggable), QSFP+, QSFPDD (QSFP Double Density), QSFP28, CFP (C
Form-Factor Pluggable), CFP2, CFP4, CFP8, CPAK, OSFP (Octal Small
Form-Factor Pluggable). The pluggable optical modules 12 operate as
an engine that converts electrical signals to optical signals or in
general as the interface to the network element copper wire or
optical fiber. Hosts for these pluggable modules include line cards
(line cards, fabric cards, controller cards, etc.) used on
switches, routers, edge products, and other network devices. The
optical modules 12 may be configured to support gigabit Ethernet,
Fibre Channel, or other communications standards. The optical
modules 12 may comprise one or more front connectors (e.g., LC or
other suitable connector) for communication with other network
devices.
[0036] The optical modules 12 are inserted into an optical module
cage. The optical module cage comprises connectors (interfaces) for
connecting the optical modules 12 with electronic components on a
line card or other electronic component (host) operable to utilize
transceivers and interface with a telecommunications network. The
cage includes a connector for one or more electronic components
that emit electromagnetic energy, and an opening configured to
receive the optical module 12 that connects to the one or more
electronic components through the connector.
[0037] The optical module cage may include openings for receiving
optical modules in a stacked or side-by-side arrangement (e.g.,
2.times.1 (two rows with one module port in each row) (stacked),
1.times.2 (1 row with two module ports) (side-by-side), 1.times.4
(1 row with four ports), 2.times.2 (two rows, two module ports in
reach row) (FIG. 1), 2.times.4 (two rows, four module ports in each
row), etc.). The term "stacked" as used herein refers to one
optical module port positioned in a location vertically above
another optical module port and the term "side-by-side" as used
herein refers to two optical module ports positioned horizontally
adjacent to one another. It is to be understood that the terms
above/below, horizontal/vertical, or front/rear are relative to the
position of the cage and also cover other orientations of the cage.
Thus, the terms are used only for ease of description and are not
to be interpreted as limiting the arrangement of ports or
components. The optical module cage may be designed for
compatibility with various optical form factors including SFP,
QSFP, QSFPDD, OSFP, CFP, CPAK, or any other current or future form
factor.
[0038] The example of FIG. 1 shows four optical module ports 16a,
16b arranged in a 2.times.2 configuration. The term adjacent
optical module ports as used herein may refer to two ports in a
side-by-side or stacked arrangement. In the example shown in FIG.
1, ports 16a are adjacent to ports 16b (i.e., each port 16a has two
adjacent ports 16b). As described in detail below, adjacent optical
module ports operate at different phases to reduce EMI associated
with the optical module port (e.g., EMI from the optical module,
optical module cage, connector, multiple ports).
[0039] The term optical module port (also referred to as port or
optical module cage port) refers to the interface at the optical
module receiving a signal and optical cage transmitting the signal
received from the physical layer device. Phases of adjacent ports
16a, 16b are constrained such that they are out of phase (i.e.,
operate at different phases, receive signals at different phases)
with neighbor ports (indicated by "+" and "-" or "0.degree." and
"180.degree." in FIG. 1) so that the combined radiation energy
cancels each other at the direction of maximum radiation. In one
example, the amplitude of the signal received at two diagonal ports
16a is 1 while the amplitude of the signal received at the other
two diagonal ports 16b is -1, wherein the amplitude of -1 changes
the phase 180.degree. for full band. As described below with
respect to FIGS. 2A and 2B, transmission (communication) of the
signals may be modified such that they are received out of phase at
the SFP 12 through physical change to specific traces between the
PHY 10 and SFP 12 or changes may be made to electrical parameters
at the PHY 10 such that the received signals are out of phase for
adjacent optical module ports 16a, 16b.
[0040] Referring now to FIGS. 2A and 2B, FIG. 2A illustrates a
physical change to traces between the PHY 10 and SFP 12 and FIG. 2B
illustrates an electrical change at the PHY to provide electrical
signals at adjacent ports that are out of phase from one
another.
[0041] The PHY 10 is in communication with the optical modules 12
through traces 20a, 20b in FIG. 2A. In one embodiment, a length of
the trace 20b between the PHY 10 and the optical module 12 is
adjusted for two of the four modules, as shown in FIG. 2A. In order
to obtain the phase offset between adjacent ports 16a, 16b, an
extra .lamda./2 length is added to the two traces 20b to increase
the length over the trace 20a. In one example, for 25 G, .lamda./2
is 6 mm in vacuum (and is shorter in PCB (Printed Circuit Board)).
The length of two of the traces may also be reduced by .lamda./2.
It is to be understood that these are only examples, and other
changes may be made to the traces to constrain the phase of
adjacent ports 16a, 16.
[0042] In another embodiment, the length of traces 22 between the
PHY 10 and SFPs 12 are uniform and an electrical parameter is
changed to implement differential port. In the example shown in
FIG. 2B, a delay (phase) is adjusted at the PHY chip 10 to
compensate skew. For example, a DAC (Digital to Analog Conversion)
parameter may be adjusted. The electrical parameter may be adjusted
at the PHY 10 to get 180.degree. phase shift for a specified
frequency, for example.
[0043] FIG. 3A is a front view of a simulation model of a 2.times.2
optical cage 30 with four modules 36. Latches 33 and light pipes 35
are openings, which allow radiation emission. FIGS. 3B and 3C are
rear views of simulation models 32, 34 showing vertical
polarization 37 and horizontal polarization 38, respectively. The
differential port embodiments described herein may be implemented
with vertical or horizontal polarization. Simulation results for
the models shown in FIGS. 3B and 3C are described below with
respect to FIGS. 5A and 5B.
[0044] As previously noted, the system may include any number of
ports. FIGS. 2A-2C illustrate simulation models with a different
number of ports. FIG. 2A illustrates differential port with a
2.times.4 arrangement of ports 36. Latches 33 and light pipes 35
are also shown. In one example, one unit (e.g., one optical module
cage in communication with one PHY) contains four ports 36, thus
the configuration shown in FIG. 2A comprises 2 units. FIG. 2B
illustrates differential port with a 2.times.8 arrangement of ports
36 (4 units). FIG. 2C illustrates differential port with a
2.times.24 arrangement of ports 36 (12 units). It is to be
understood that these are only examples and the network device may
be configured for receiving any number or type of optical
transceivers arranged in any format.
[0045] FIGS. 5A, 5B, and 6 contain graphical plots 50, 52, 60,
respectively, showing a comparison of electromagnetic radiation
from a conventional port arrangement (referred to as common port)
in which the phases of four SFP ports (1 unit) connected to a PHY
are in phase, to a differential port configuration described
herein. Directivity (dB) is plotted against frequency (GHz). FIG.
5A illustrates directivity for 2.times.2 ports with vertical
polarization (FIG. 3B). FIG. 5B illustrates directivity for
2.times.2 ports with horizontal polarization (FIG. 3C). FIG. 6
illustrates directivity for 2.times.24 ports (FIG. 4C). As can be
seen from the graphs, radiation (EMI) with differential port is
less than that of conventional common port across all measured
frequencies. In almost full band, differential port is about 3 dB
better than common port. Based on example simulation results, it
was found that for any unit number, any polarization, any phase
delta between units, differential port provides about a 3 dB
improvement over common port in almost full band.
[0046] In application, different PHY may have different relative
phase and the phase delta may be random and uncontrolled. In one
example, a 2.times.4 simulation model had a phase of a first unit
(four ports) set to 0.degree. and the other unit (four ports) set
to x.degree.. Simulation results for x.degree.=45.degree. showed an
approximately 3 dB improvement of differential port over common
port. Simulation results for x.degree.=90.degree. showed an
approximately 3 dB improvement of differential port over common
port. For x.degree.=180.degree., adjacent units are differential
units and EMI is reduced. Differential port still showed an
approximately 0.5 dB improvement. Differential unit (phase delta
between adjacent unit=180.degree.) was found to provide
approximately a 2 dB improvement over common unit (phase delta
between adjacent unit=0.degree.).
[0047] The following describes broadband performance for random
phases. Three sets of random phase combinations (Random-1,
Random-2, Random-3) (ranging from 0 to 360 degrees) as shown in
table 70 of FIG. 7A and graphical plot 72 of FIG. 7B, were applied
to a simulation model with 2.times.24 ports for common port and
differential port. Each unit (1-12) (each unit comprising 4 ports)
implements one random phase. In this example, the phases are
implemented in 10 G, with 10 G being the lowest frequency and
higher frequencies more random than 10 G. Graphical plots 80, 82,
84 in FIGS. 8A, 8B, and 8C illustrate performance results for the
Random-1, Random-2, and Random-3 phases, respectively. As shown in
FIG. 8A, with random phase combination 1, differential port is
about 2-6 dB better than common port. As shown in FIG. 8B, with
random phase combination 2, differential port is about 1-4 dB
better than common port. As shown if FIG. 8C, with random phase
combination 3, differential port is about 1-4 dB better than common
port.
[0048] The embodiments described herein may operate in the context
of a data communications network including multiple network
devices. The network may include any number of network devices in
communication via any number of nodes (e.g., routers, switches,
gateways, controllers, edge devices, access devices, aggregation
devices, core nodes, intermediate nodes, or other network devices),
which facilitate passage of data within the network. The network
devices may communicate over one or more networks (e.g., local area
network (LAN), metropolitan area network (MAN), wide area network
(WAN), virtual private network (VPN) (e.g., Ethernet virtual
private network (EVPN), layer 2 virtual private network (L2VPN)),
virtual local area network (VLAN), wireless network, enterprise
network, corporate network, data center, Internet, intranet, radio
access network, public switched network, or any other network).
[0049] FIG. 9 illustrates an example of a network device (e.g.,
switch) 90 that may implement the embodiments described herein. In
one embodiment, the network device 90 is a programmable machine
that may be implemented in hardware, software, or any combination
thereof. The network device 90 includes one or more processor 92,
memory 94, ports (interfaces) 96 configured to implement
differential port as described herein, and physical layer device
98.
[0050] Memory 94 may be a volatile memory or non-volatile storage,
which stores various applications, operating systems, modules, and
data for execution and use by the processor 92. The network device
90 may include any number of memory components.
[0051] Logic may be encoded in one or more tangible media for
execution by the processor 92. For example, the processor 92 may
execute codes stored in a computer-readable medium such as memory
94. The computer-readable medium may be, for example, electronic
(e.g., RAM (random access memory), ROM (read-only memory), EPROM
(erasable programmable read-only memory)), magnetic, optical (e.g.,
CD, DVD), electromagnetic, semiconductor technology, or any other
suitable medium. In one example, the computer-readable medium
comprises a non-transitory computer-readable medium. The processor
92 may process data received from the ports 96. The network device
90 may include any number of processors 92.
[0052] The physical layer device (chip) 98 drives a plurality of
ports 96. As previously described, there may be more than one
physical layer device, each driving a plurality of optical module
ports.
[0053] The network may comprise any number of interfaces
(linecards, ports) for receiving data or transmitting data to other
devices.
[0054] It is to be understood that the network device 90 shown in
FIG. 9 and described above is only an example and that different
configurations of network devices may be used. For example, the
network device 90 may further include any suitable combination of
hardware, software, algorithms, processors, devices, components,
interfaces, or elements operable to facilitate the capabilities
described herein.
[0055] As can be observed from the foregoing, one or more
embodiments provide improvement over conventional systems. For
example, one or more differential port embodiments described herein
may improve EMC radiation performance by about 1-6 dB over common
port without incurring extra cost over existing solutions. In
simulation tests, differential port shows an improvement in 3D
radiation pattern and 2D radiation pattern for a phase delta or
random phase, as can be observed in polar plots showing radiation
pattern. In common port, energy is concentrated on one side in
front of a panel, whereas with differential port, energy is divided
among four parts so that Emax (maximum energy) is smaller. The
embodiments may be implemented in any type of network device (e.g.,
switch, router) with any number of ports and for any phase
distribution. As previously described, differential port may be
implemented through a physical change (at trace) or an electrical
parameter change (at PHY).
[0056] Although an apparatus and method have been described in
accordance with the embodiments shown, one of ordinary skill in the
art will readily recognize that there could be variations made
without departing from the scope of the embodiments. Accordingly,
it is intended that all matter contained in the above description
and shown in the accompanying drawings shall be interpreted as
illustrative and not in a limiting sense.
* * * * *